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F35 to display in the UK this year.

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F35 to display in the UK this year.

Old 28th Apr 2014, 12:27
  #61 (permalink)  
 
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Correct me if I am wrong, but I seem to remember a fairly critical limit speed when "hitting" the ramp (this was a 12 degree model) that was due to nose wheel strength limitations with the Harrier.

I wonder if the F35 (B) will be similarly limited or whether the nose gear is sufficiently strong for this not to be a problem. Maybe with a longer deck (on the QE2 class) the transition from flat-deck to ramp incline will be more gradual for this not to be an issue.

A 55,000 lbs T/O mass is quite a big increase for the F35 from the Harrier II (which itself was a lot heavier than the GR3/Sea Harrier) and only 3-5,000 lbs less than the max weights allowed for the F4 and Buccaneer which ISTR were 58,000 and 60,000 lbs respectively.

Just curious.....

MB
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Old 28th Apr 2014, 13:36
  #62 (permalink)  
 
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If memory serves the 'convertible' carrier was the original 300m and then 290m designs. The government then insisted on more budget cuts and forced a redesign to a smaller version, they then realised that that smaller craft had a poor sortie rate so forced another redesign up to the current 280m version. Along the way the ability to change launch systems was dropped which the government OK'd as it saved a few pennies.

So in brief, various governments introduced years of delays and cost increases due to constant re-design and engineering work while going about trying to save money in some of the most stupid ways possible.

At the height of the nonsense when the press and public was questioning what was going on the government of the day conviently forget it was them who changed the design brief and agreed to the dropping of various features.
Not quite.

The current design (design Delta) remains perfectly capable of being converted to catapult & arrester gear configuration. The general arrangement drawings for the ship show the space allocation for the systems quite clearly and you can see the spaces if you walk round the actual ship.

The problem is that once the arrangement drawings had been completed in 2004, no further detailed work on the CV design was contracted for, although the overall design config control was maintained. Essentially, while the design is capable of being converted, no-one asked the Alliance to actually progress the detail of that design (ie produce the detailed system and component level design information to allow people to actually produce the equipment items and install them on the ship). Part of that was reluctance (by the US) to release EMALS info to some degree because at that stage it didn't exist and also our favourite FLA - ITAR. But mainly because both RN and RAF were still treating the CV option as a potential fall-back rather than a serious option.

What that meant, was that when the CV-reversion was requested, production of the required design information would have meant either stopping work on the second ship and waiting for design info (while paying for the workforce, courtesy of TOBA) or progressing the ship but then tearing chunks of it out again to fit EMALS/EAR. That is why the projected cost is so high, when a rational look at the work content just to include those systems in the ship would never get anywhere near the £1.8Bn figure quoted.

So no design features were dropped, it's just that the MoD did not fund the detailed elements of the design process that would have allowed the ships to complete as CV-capable at an acceptable price. primarily a commercial / programme issue rather than technical.
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Old 28th Apr 2014, 15:34
  #63 (permalink)  
 
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Thanks, Mr Boffin.

Engines - Interesting note on the roll posts - I'm not sure that has been out before (and checking, it was not in a quite detailed brief from early 2009).

Haraka - Of course it's not a Yak-141 Freestyle knock-off. I mean, the 141 could not do a VL demo at Farnborough without damaging the runway . Conversely, one also remembers when lift-plus-lift/cruise was dismissed as old hat, and doubtless far heavier than the bold new shaft-drive technology.
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Old 28th Apr 2014, 16:06
  #64 (permalink)  
 
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Wonder if they've applied for the ITAR to bring it to UK, usually takes a year or two!

EG
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Old 29th Apr 2014, 07:57
  #65 (permalink)  
 
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It's my understanding that ITAR applies to export, not visits, displays, etc. Of course, there will already be technology transfer agreements in pace for certain nations under FMS or partnership agreements. My understanding, anyway.
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Old 29th Apr 2014, 10:22
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Madbob,

Good question on the ski jump landing gear loads - perhaps I can help.

The landing gear layouts on the Harrier and the F-35 are fundamentally different, especially in the nose leg area. The Harrier has a 1950s style 'bicycle' or 'tandem' layout, and the weight of the aircraft is split almost 50/50 between the aft leg (we called the 'main') and the forward leg (which we called the 'nose leg').

What this meant for Harrier ski jump ops was that the front leg was fairly heavily loaded. We increased the liquid spring pressure for ski jump ops, and the limiting condition was to avoid total closure of the nose leg spring as it reached the end of the ski jump. (The leg started closing as it entered the ramp, and closed steadily as it approached the exit lip).

The F-35 has a more conventional 'tricycle' layout, with the two main gears taking around 90% of the load, the nose leg taking around 10%. The early checks on ski jump profiles and predicted launch speeds showed that the nose leg loads during ski jump launches were well within the highest design load, which was driven (I think) by vertical landings, with an arrival on the nose leg as the worst case, or with high lateral drift. the forthcoming tests at Pax will provide the real data.

LO's point about lift plus lift/cruise options for STOVL aircraft points to a key aspect of the JSF/F-35 project. The basic physics of powerplant technology have driven the choices available to the teams who were required to produce a large single engined single seat aircraft. (As I've posted a few times, the single engine requirement was a key driver set by US DoD staffs who wanted to avoid the weight and cost overruns associated with a slew of failed US twin engined projects in the 70s and 80s).

In the end, the Harrier concept (a large engine in the middle of the aircraft providing both lift and cruise via vectoring arrangements) just couldn't be taken forward to meet the JSF requirements. There wasn't enough lift at a reasonable weight from hot jets, and the hot gas ingestion problems were insurmountable. Lastly, having an engine in the middle of the aircraft just couldn't be reconciled with an effective supersonic strike/fighter aircraft. Kingston battled to produce a workable design all through the 70s and the 80s, and Boeing's X-32 proved the point.

The LM solution was built around a separate lift device located forward using cold air to deliver thrust as efficiently as possible, which also offered a solution to the hot gas ingestion problem. This allowed optimal location of the main engine at the rear. A number of options for driving the lift fan had been tested between the 60s and the 90s (including gas drive, and even electrical), but in the end, shaft drive offered the lightest and lowest volume solution.

As I've often posted, it's good that people question and criticise the F-35 programme. I hope that my posts help them understand the basic physics behind the issues and also to understand just how challenging the choices are that have to be made early on in a combat aircraft programme.

Best regards as ever to all those making the hard calls out there now,

Engines
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Old 29th Apr 2014, 13:55
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One has to wonder whether the shaft-driven (SDLF) system ended up saving any weight or money versus the separate lift engine (LPLC).

SDLF eliminates a (small) turbine gas generator but adds a shaft, gear and clutch. It also drives weight into the main engine (bigger LPT and shaft) where LPLC does not, and it tends to push you towards a shorter (hence fatter) body because you want to constrain shaft weight, volume and number of bearings. I should think that digital engine controls would still allow you to use differential throttle for pitch control in hover.

The Macs proposal was LPLC, of course, but there was substantial prejudice against that solution and there were other aspects of that offering that weighed against the team. (They had come together rather late in the game.)

It's all spilled milk of course - about 12 billion gallons or about 90 loads on this:
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Old 29th Apr 2014, 15:31
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LO (and others)

The main issues, in my view, with a separate lift engine were these:

1. A separate jet lift engine had to use hot air to develop thrust - that's inherently less efficient than using cold air. That reduces the basic efficiency (and weight) advantage of a separate engine.

2. A hot engine exhaust located towards the front of the aircraft will inevitably introduce hot gas ingestion effects. As LM have shown, the cold lift fan provides a useful way of helping get past a very serious problem.

Having looked at a couple of papers recently, it looks as if the Gas Coupled Lift Fan (GCLF) was a very serious contender within NG/BAE until late in the day, when it became clear that the piping and ducting required to drive a large (c. 18,000 lb thrust) fan would place too much volume demand on the fuselage design. LM appear to have gone fro shaft drive from early on.

As I've said before, the designers have to make some very big calls early on for powered lift aircraft. In my view, LM got most of them right, given the requirements they had to meet. Others are happily invited to disagree.

Best Regards as ever to those working the sums,

Engines
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Old 29th Apr 2014, 21:01
  #69 (permalink)  
 
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Wasn't this the thread about F-35 going to display in the UK this year? I don't suppose it's coming to France, is it?
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Old 30th Apr 2014, 06:55
  #70 (permalink)  
 
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Thumbs up

Nice one courts, happy days to ya.

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Old 30th Apr 2014, 14:51
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For those interested in how LM was able to win the JSF program, please look at the history of the Advanced Short Take-Off/Vertical Landing (ASTOVL) program.

McDonnell –Douglas had the top two (ASTOVL) proposals (one for gas-coupled lift fan and one for shaft-coupled lift fan). DARPA told McDonnell to move forward with the gas-coupled lift fan using the GE YF120 engine (which later was developed into the General Electric/Rolls-Royce F136). DARPA then funded LM to work on the shaft-coupled design using the P&W F119 engine (which was developed into the P&W F136). McDonnell actually built a full-scale design to house and test a gas-coupled lift fan when the program was terminated and the JSF program was started.

While McDonnell was developing its proposal for the JSF program, it was told that the decision had been made to use the P&W engine and that McDonnell would have to include the cost of developing the GE YF120 engine into their program cost estimate. At that point there was little time to do anything except bring Northrop on board with a separate lift engine.

So that is also the story of how DARPA eventually caused the demise of McDonnell Douglas, forcing it to merge with Boeing.

(Sorry Courtney, but since it was brought up…..)
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Old 30th Apr 2014, 18:04
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Bevo - That's interesting. The story from Paul Bevilaqua is that the SDLF evolved from tandem-fan ideas (not unlike the way that the Harrier evolved from the Wibault Gyroptere) at Lockheed Skunk Works. At the point where I became cognizant of the whole remote-drive fan idea (1991ish) it did already seem that Macs and GE were teamed on the GDLF.

However, it's also quite possible that such teaming was directed from on high.

Engines: I don't know that either system (LPLC or SDLF) is inherently more efficient than the other one. It depends on the BPR of the lift engine (which appears to be lost in the mists of time as far as the GEA-FXL design goes). Of course lower BPR=hotter, but it also means lower diameter and a more slender front end. Then again, it allows the back end to run cooler (mixed flow).
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